The present invention relates to gas compressors, and more particularly to inlet control valves for gas compressors.
Inlet control valves are commonly used on gas compressors to regulate compressor capacity. These valves control the capacity by limiting the intake air that enters the compressor. An unloader valve is a valve that loads and unloads the compressor, and is often used as an inlet control valve. An compressor unloader valve is xe2x80x9cloadedxe2x80x9d when the valve is open and gas can pass through it, and xe2x80x9cunloadedxe2x80x9d when the valve is closed and blocks the flow of gas into the compressor.
Pneumatic, hydraulic, and electronic methods have been used to open and close unloader valves. Several unloader valves are two-position valves and only have an open position and a closed position. These valves are not able to modulate to positions between these two extremes, and this limited number of settings can reduce the effectiveness of a compressor.
Additionally, pneumatic unloader valves typically use some type of a piston and cylinder configuration to open and close the valve, and can suffer from a xe2x80x9cstick/slipxe2x80x9d problem between sliding surfaces sealed with O-rings. The initial force necessary to overcome the static friction between the sliding surfaces of the piston and cylinder is often greater than that needed to overcome the sliding force. Therefore, a larger force must be applied to initially move the piston, but once it is moving, the resistive force is not as large and the piston moves too far.
The stick/slip problem is not of great concern for two-position valves because they are only moving between two extreme positions from the open position to the closed position, and do not stop in between. However, this can be a serious problem with modulating valves because it creates erratic piston movement that is segmented, or choppy, not the smooth controlled movement needed for a modulating valve. The piston will generally move past the desired position, and must be brought back to the proper location.
A problem experienced in oil-flooded compressors is backflow of a gas and oil combination through the air inlet. Backflow can take place when a compressor stops while the system is still pressurized. In this situation, the compressor system has a higher pressure than the atmospheric inlet, so the gas and oil mixture can be forced toward the lower pressure and out the inlet. Prior art arrangements seek to solve this problem by utilizing spring loaded check valves that only allow one-directional flow. These additional check valves are effective, but they increase the cost and complexity of a compressor.
Noise reduction also a concern with gas compressors. Some prior art unloader valves allow the internal noise of the compressor to escape through the inlet valve while it is open. Inlet valves that provide a straight path from the air intake to the compressor are relatively loud because there are fewer mechanisms to block noise as it exits through the valve.
Another noise problem for compressors is known as xe2x80x9crotor rumblexe2x80x9d in the industry. This condition occurs when the control valve is unloaded and pressure builds up in the compressor system. Compressors generally relieve this pressure by discharging xe2x80x9cblowdownxe2x80x9d air. In an oil-filled compressor, the blowdown air is an air and oil mixture and can cause contamination if it is discharged into the atmosphere, or into the compressor package. Some compressors solve this problem by piping the blowdown air to discharge into the intake valve downstream from the air intake filter. Since this cavity is at atmospheric pressure, and the blowdown air is at a higher pressure, the blowdown air expands suddenly and produces an undesirable noise.
The invention provides an air compressor including a pneumatic modulating inlet unloader valve that does not experience stick/slip, prevents backflow, prevents rotor rumble, and reduces the noise of blowdown air. The inlet unloader valve includes a housing with a main chamber, a housing inlet, and a housing outlet. Air enters the housing through the housing inlet and exits the housing through the housing outlet. A piston chamber is located within the main chamber, and a piston is at least partially disposed in the piston chamber. The piston is movable within the piston chamber toward and away from the housing inlet.
A valve disc is mounted to the piston, and is movable with the piston. A valve seat is disposed near the housing inlet, and the valve disc contacts the valve seat to create a seal and close the inlet valve. The valve disc is mounted around the piston, and a spring biases the piston towards the closed position and holds the valve disc against the valve seat. The inlet valve is closed, or xe2x80x9cunloadedxe2x80x9d when the valve disc contacts the valve seat, and open, or xe2x80x9cloadedxe2x80x9d, when the valve disc is separated from the valve seat. Preferably, the inlet valve is normally in the closed position.
The valve disc has an aperture and a flexible member that comprise a plate valve. The plate valve selectively provides air flow from the housing inlet into the main chamber, and the flexible member can contact the valve disc to close the apertures. When the pressure within the compressor reverses, the plate valve preferably seals the apertures to prevent backflow.
A piston retainer preferably surrounds a portion of the piston, and is also disposed within the piston chamber. A control cavity is disposed within the piston chamber, and is at least partially defined by the piston, the piston retainer, and the piston chamber. The control cavity preferably creates a space between the piston and the piston retainer in which a pneumatic signal can be injected to separate the piston from the piston retainer. A control port is interconnected to the housing, and a control inlet runs through the control port and is in fluid flow communication with the control cavity. The pneumatic signal passes through the control inlet and into the control cavity.
The pneumatic signal is used to control the position of the piston. The pneumatic signal works against the spring and moves the piston away from the housing inlet. When the piston moves away from the housing inlet, the valve disc moves with it and separates from the valve seat. The inlet valve can preferably be opened, closed, and placed in any position using a pneumatic signal.
Air compressors must often discharge air to relieve internal pressure. The discharged air is commonly called blowdown air, and creates an undesirable noise if it is vented to an area at a lower pressure. The inlet valve preferably has a blowdown port with a silencer interconnected to the housing inlet where the blowdown air can be discharged. Preferably, the blowdown air is drawn back into the compressor through the plate valve, so any oil or contamination in the blowdown air is contained within the compressor system. The silencer has multiple apertures to breakdown the air stream into multiple smaller streams and dissipate the noise often caused by venting the blowdown air.